This invention is concerned with producing fused polymeric articles, more particularly with a process for the manufacture of fused polymeric articles comprising depositing a quantity of particles of heat-fusible polymeric material in a three-dimensional configuration on a receiving surface, heating the deposited material and subsequently cooling it thus to provide a fused polymeric mass which retains said configuration, and removing the fused mass from the receiving surface, and with a material suitable for use in carrying out such a process.
One such process is described in US-A--4,480,581 wherein three-dimensional polymeric articles are produced by depositing, e.g. by screen printing, a three-dimensional pattern of a polymeric powder on a support surface provided by an annular belt or web, which pattern is then transported to a heating station where the powder is fused and the fused mass is then transported to a cooling station where another substrate may be pressed on, or otherwise joined to, the surface of the mass. At the cooling station, the fused three-dimensional polymeric article is lifted or otherwise removed from the support surface by suitable transfer means. Polymeric powders suitable for use in the process and apparatus disclosed and claimed in the above-mentioned patent specification include polyolefins, polyesters, polyamides and polyurethanes.
The support surface provided by the annular belt or web is provided with a smooth reinforced film of polytetrafluroethylene or the like, but nevertheless in practice it has been found necessarv or at least desirable to apply a release agent to the support surface carrying the pattern of polymeric powder, tnus to prevent adhesion of the surface of the fused mass to the support surface and to facilitate the removal of said mass from said support surface. While release agents perform an important function, their use presents undesirable operational features, in particular in that the application of the release agent to the belt is time-consuming and waste can result if the release agent is not applied properly, and also the release agent can stain the final polymeric article.
The object of the invention is thus to provide an improved process for the manufacture of fused polymeric articles, and an improved particulate polymeric material for use in carrying out such process, wherein the problems arising out of use of release agents in producing polymeric articles from polymeric powders are overcome.
This object is resolved, in accordance with the present invention, in a process as set out in the first paragraph above, in that each particle has a coating of a release agent and in that, when the material is heated to fusion temperature, the release coating is exuded to the surface of the fused mass to provide a release coating about the surface of the mass, thus facilitating removal of the latter from the receiving surface.
It will thus be appreciated that, by thus providing the release agent on each particle, firstly the agent is applied without requiring the expenditure of time or effort on the part of the operator, furthermore it is applied only in the region where it is required and furthermore exhibits better adhesion to the article than to the support surface so that it is removed cleanly, and, as a consequence, the risk of staining of articles being made by this process is significantly reduced.
More particularly, in carrying out the process in accordance with the invention the fused mass is removed from the support surface while the average temperature of the fused mass is near or above the Vicat temperature of the polymeric powder; the Vicat temperature of the polymeric powder is measured by the ASTM D1525-76 Rate B Standard Test Method For Vicat Softening Temperature of plastics.
One embodiment of the present invention relates to producing reinforcing or stiffening elements for footwear such as counters, box toes or the like, the preferred polymeric powders in this case being ionomeric polyolefins, particularly those of the type described in detail in US-A-3,264,272, which are essentially ionomeric copolymers comprising ethylene and polymerizable monomers containing carboxylic acids, sold commercially by E. I. DuPont de Nemours & Co. under the registered trademark SURLYN. Other polymeric powders useful in preparing footwear stiffener reinforcing elements are nonionomeric polyolefins such as polyethylene, polypropylene and the like and copolymers of olefins with such monomers as vinyl acetate, ethyl acrylate and the like. Ethylene copolymers of the type described in US-A-3,239,370 are also suitable in the practice of the invention, as are mixtures of polymers and copolymers mentioned before. The particle size of the polymeric powder for footwear stiffener reinforcing elements can vary and suitable particle sizes include those which will pass through about a 10 to about a 120 mesh screen. Particularly preferred particle sizes for the SURLYN ionomeric olefin copolymer powders are those which will pass through a 20 to about a 40 mesh screen.
Preferred release agents for use in the process in accordance with the invention are silicone mould release agents which are preferably organo-polysiloxanes having low surface tension so that the agent can sufficiently wet surfaces to provide release of moulded polymeric articles from surfaces carrying the articles. The especially preferred release agents furthermore are "paintable" silicones. paintable silicone release agents need not be removed or are more readily removed from the surface of the fused article in order to effectively apply paints or adhesives to the surface. Obviously if removal of the release agent from the surface of the fused article is not contemplated or needed, non-paintable silicone release agents can be suitably employed. Preferred silicone release agents are at least partially miscible in the antistatic agent at least at the temperature of fusion. Paintable alkyl and/or aryl polysilozane relase agents are especailly preferred, such release agents being commercially available and known to the art. Preferably the amount of mould release agent used lies in a range between about 0.01 and about 0.5, more particularly from about 0.05 to about 0.2, percent by weight release agent based on the total weight of the polymeric powder and the antistatic, release and anti-agglomeration agents. The ratio of the respective amounts of the preferred antistatic agent to the preferred release agent can vary but the most effective ratios are between about 2:1 and 2:3.
Preferably in accordance with the invention the polymeric powder is mixed with a blend of the silicone release agent. and an antistatic agent together with an anti-agglomeration agent. (Most polymeric materials have good electrical insulating properties but because of their non-conductivity they easily acquire but do not readily lose static electrical charges). Preferred antistatic agents are external antistatics which operate primarily by conductance. They include dissolved ions and are present on the surface of the polymeric powder and are hygroscopic. Accordingly they provide a conductive path consisting of a thin layer of water which the antistat absorbs from the atmosphere onto the surface of the polymeric powder. The conductivity of the absorbed water is significantly increased by the presence of the dissolved ions thereby increasing the overall effectiveness of the antistat. Preferred external antistats suitable in the practice of the present invention include cationic compounds, anionic compounds and non-ionic compounds. Cationic antistat compounds include quarternary ammonium or phosphorium salts in which the quarternary group may also form part of a ring (e.g. imidizoline); the anion may be chloride or meta-sulphate for example. Anionic antistat compounds include alkyl sulphates, sulphonates, phosphates, dithiocarbamates and carboxylates; the cations are usually alkali metals or alkaline earth metals. Non-ionic antistat compounds include polyethylene glycol esters or ethers, fatty acid esters or ethanolamides, mono and diglycerides and hydroxyethylated fatty amines. Especially preferred antistats are quarternary ammonium salts. Internal antistats or electrical fields or other techniques can also reduce the static charges on the polymeric material but external antistats present the most inexpensive, effective and convenient manner for minimizing the effects of static charges in the polymeric material. The amount of external antistatic agent used will depend primarily on the particle size of the polymeric powder. Preferably, effective amounts of antistatic agent range from about 0.01 to about 0.5, more particularly from about 0.05 to about 0.2, percent by weight of antistatic agent based on the total weight of particulate polymeric material and the antistatic, silicone release and flow promoter agents.
Anti-agglomeration (anti-caking, antibridging) or dryer or flow promoter agents useful in the practice of the invention are those which can be substantially uniformly dispersed in or carried by the monomolecular layer of the antistatic and release agent mixture coating the polymeric powder. Essentially the function assigned to the anti- agglomeration agent is to hold the individual polymer particles apart and prevent intimate contact between the particles and to "lubricate" the particle surface to in effect provide "bearings" upon which the individual particles can move relative to each other. Anti-agglomeration agents useful in the practice of the invention are those which will at least soften and preferably melt at or below the temperature for fusing the polymeric powder. Preferred anti-agglomeration agents are organo metallic soaps, fatty acids and waxes which will melt at or below the fusing temperature. Metallic stearates particularly zinc or magnesium stearates are the especially preferred anti- agglomeration agents. Preferably the amount of the metallic stearate anti-agglomeration agent lies in a range between about 0.05 and about 1, more particularly 0.2 and 0.6, percent by weight of the agent based on the total weight of powder and antistatic, release and anti-agglomeration agents.
It will, however, be appreciated that these agents need not be used if suitable flow or antiagglomeration performance characteristics can be achieved in other manners, e.g. by way of specialised processing techniques and/or specialised materials which eliminate the need for anti-agglomeration agents.
It is believed that the preferred antiagglomeration agent is substantially uniformly dispersed in at least one of the agents in the mixture of antistatic and silicone release agent coating the polymeric powder during fusion of the powder. At the fusion temperature, the preferred anti- agglomeration agent softens or melts and is miscible or otherwise dispersed in the antistatic agent and/or silicone release agent to provide a substantially uniform dispersion of antistatic agent, silicone release agent and anti-agglomeration agent which is distributed in continuous fashion about the surface of the polymer particle. As fusion proceeds, some of the dispersion may be entrapped internally at the interstices of the fused particles but a sufficient portion of the dispersion is exuded to the surface of the fused molten mass to provide a release coating about the surface of the fused mass. On cooling the fused mass, the release coating coalesces or coagulates to form a thin, gel or wax-like coating continuously distributed about the surface of the fused mass. The gel or wax-like character of the coating assures and enhances release of the fused mass as a dimensionally stable polymeric article from the support surface carrying the mass, preferably while the average temperature of the mass is near or about the Vicat temperature of the polymeric powder. If a paintable release agent is employed, the coating provided by the coalesced residue of the dispersion of the agents need not be removed from the surface. Instead, hot melt adhesives for example, can be applied directly to the surface of the polymeric article for bonding the surface to the surface of another substrate.
Depending upon the end use of the polymeric article, pigments and/or fillers and/or other such additives can be included in the polymeric powder and/or mixed with the polymeric powder.
This invention further provides, in its material aspects, a material for producing fused polymeric articles comprising heat-fusible, flowable, substantially non-agglomerating particulate polymeric material which is a non-ionomeric polyolefin, an ionomeric polyolefin or a mixture of these, said fusible particulate polymeric material being coated with a silicone release agent so that when the polymeric material is heated to fusion temperature, the resulting fused polymeric mass has a silicone release coating on the surface of the mass which permits removal of the mass from a support surface carrying the mass.
The invention as well as manners for making and using the invention will be more fully appreciated from the following non-limiting Examples presented for the purpose of illustrating the invention.
The following ingredients were charged to a Patterson Kelly Twin Shell Dry Blender (Model 20) with a beater bar:
The ingredients were mixed at room temperature for 25 minutes at a shell speed of about 25 rpm and at a beater speed of 2160 rpm. The mixer was stopped and 828 grams of zinc stearate 4 were then added to the ingredients and mixing was resumed for 5 minutes at the same speeds.
The polymeric powder product comprised discrete non-agglomerated powder particles and has satisfactory cold flow (anti-caking and anti-bridging) properties.
Example 1 was repeated but 828 grams of magnesium stearate were substituted for the zinc stearate. The magnesium stearate used was PETRAC mg-20 N.F. having a softening point of about 140°C and sold by Petrochemicals Company Incorporated.
While Dow Corning 230 Fluid is used as the silicone release agent in Examples 1 and 2, other silicone release agents such as Dow Corning 200 Fluid and Dow Corning 203 Fluid for example are suitable silicone release agents. Dow Corning 200 is a polydimethylsiloxane while Dow Corning 203 is an alkylaryl polysiloxane. Dow Corning 203 is paintable but Dow Corning 200 is not.
The polymeric powders of Examples 1 and 2 were used in production scale runs on multistation apparatus as described in U.S. Patent 4,480,581 to provide a plurality of reinforcing elements for shoe uppers. In each run, a three-dimensional pattern of the powder was deposited onto the annular receiving belt (support surface) at a powder deposition station including a stencil assembly in the manner described in U.S. Patent 4,480,581. The annular receiving belt was rotated to an arcuate heating station, as described in the patent, where the polymeric powder pattern was fused at a temperature of about 249°C (480°F) to about 260°C (500°F) for 25 seconds. The fused mass was then moved to a join and cool station as described in the patent where a shoe upper substrate was pressed against the mass by transfer means causing the fused mass to press against a cooling plate arranged beneath the receiving belt. During the runs, the temperature of the cooling or chill plate was between about 32°C (90°F) to about 43.3°C (110°F) and the mass was pressed against the plate for about 2.5 seconds. Transfer means removed the reinforced shoe upper from the receiving belt as described in the above mentioned patent. Average temperature measurements of the fused mass were made substantially immediately (within about one second) after removal of the mass from the surface of the belt by the transfer means. The average temperature of the surface of the fused element removed from the belt was measured using a Wahl HEAT SPY, infra-red thermometer, Model DHS-16 sold by Wahl Instruments Incorporated. Ayerage temperature measurements of the surface of the reinforcing element ranged between 107.2°C (225°F) and 126.7°C (260°F) which is about 44.4°C (80°F) to about 63.9°C (115°F) above the Vicat temperature of the SURLYN polymeric powder providing the reinforcing element.
In the runs, reinforced shoe uppers were produced at the rate of 360 pairs per hour. No release agent was applied to the receiving belt at any time during the run and the reinforcing elements were readily removed from the belt without any interruption throughout the operation. The reinforcing elements, which were about 0.09 cm (0.035, inches) thick, exhibited excellent physical properties, and particularly an excellent combination of tear strength and elongation properties. Also hot melt or latex adhesives could be applied directly to the surface of the reinforcing element of the shoe upperto effectively assemble the shoe upper without any cleaning or other conditioning of the surface.
While the preferred embodiment of the invention involves the preparation of three-dimensional reinforcing agents for shoe stiffener materials as described, the polymeric powders of this invention can be use to provide various polymeric articles in various ways. For example, the polymeric powders can be used to provide various reinforcing or stiffening elements for apparel such as shirts, sports clothing or for sports equipment such as pads, gloves, caps with visors or the like. Accordingly, the polymeric powders can proyide a wide variety of three-dimensional polymeric articles having various sizes, shapes and end uses.
The preferred novel polymeric powders presented to the art by the present invention have the capability to provide three-dimensional fused polymeric articles which can be removed from a support surface carrying the article as dimensionally stable articles while the average temperature of the fused mass is near or above the Vicat temperature of the polymeric material. Dimensionally stable means that, although the article has not completely solidified, it will not undergo significant distortion such as elongation or tearing and can retain substantially the same dimensional size and shape during and after removal until complete solidification. Removal of the polymeric article from thhe support surface near or above the Vicat temperature is a definitely preferred embodiment of the present invention. The feature provides obvious advantages in high speed, commercial production processes for polymeric articles. However, it should be understood that processes involving removal of the polymeric article from the support surface below the Vicat temperature are included within the scope of the present invention.